横向管间距对涡强化扁管管片局部传热的影响

应用萘升华传质/传热比拟技术研究了横向管间距对涡强化扁管管片局部传热的影响.通过对不同位置的横向实验数据进行比较,反映了在纵向放置不同旋转方向的涡产生器情况下,不同横向管间距(S1/S2=0.582、0.727、0.969)的局部传热特性.     

管间距对翅片管换热器热力性能的影响

分析了翅片管换热器传热及流动阻力性能的影响因素;叙述了场协同理论的基本机理,并与等流速排列方式联系起来加以分析讨论;概述了翅片管换热器研究中管间距对传热及流动阻力影响的国内外研究现状;讨论了不同翅片及基管类型结构尺寸下管间距对换热器传热及流动阻力影响的规律。在此基础上,对管束排列的研究前景进行了展望。     

基于质量积耗散的膜法除湿组件结构设计

建立了错流中空纤维膜液体除湿组件的二维传热、传质数学模型,引入研究传质过程质量积耗散的湿阻来衡量溶液除湿过程中水分传递的不可逆性。通过分析膜法除湿组件中除湿与传热耦合的湿空气水分传递过程,得到了热湿传递过程中传质的阻力表达式。通过一个典型设计实例,得出了可以降低中空纤维膜除湿组件不可逆传质损失的管长、根数、管间距、排列方式等设计参数。     

蒸发式冷凝器管外流体流动与传热传质强化

蒸发式冷凝器是一种高效散热设备,能源危机和水环保促进了它的应用.提出了扭曲管强化管外水和空气流动及传热传质,测试了圆管、椭圆管、扭曲管等三种水平管蒸发式冷凝器的流动与传热传质性能,结果表明,扭曲管间为有序的可控制水流,分布均匀,脱落速度快,更易形成柱状流,管表面水膜厚度比现有圆管和椭圆管小;传热传质系数随冷却水喷淋密度及风速的增大而增大,但冷却水喷淋密度增大至一定值后,对传热传质系数基本没有影响;扭曲管的传热传质系数高于椭圆管,特别是圆管,总结了扭曲管传热传质系数经验式.     

空气横掠椭圆矩形翅片管束的放热和阻力性能的试验研究

本文根据十种椭圆矩形翅片管束的放热和阻力性能的试验数据,用线性回归分析和F水平显著性检验方法求得了椭圆矩形翅片管束的气侧放热和阻力性能的关联式 NuPr~(1/3)=0.09N~(0.093)Re~(0.557)[(S_1-d_(r,t))/d_(r,t)]~(1.07t)[(S_1-d_(r,t)/(S_2-d_(r,t))]~(-0.364) f=2.95N~(0.173)Re~(-0.244)[(S_1-d_(r,t))/(S_2-d_(r,t))]~(-0.15r) 本文还据此确定了这类管束分别在最小容积和最小迎风面积标准下相应的最佳横向管间距和纵向管间距。最后,将本文求得的二种“最佳”结构换热器与某种等间距结构(S_1=S_2=0.0605m)换热器进行综合性能比较,得出了对设计具有一定参考价值的结论。     

错排环布圆管翅片式换热板芯的实验研究

本文利用传热传质之间的比拟关系研究了错排环布圆管换热板芯的平均传热特性及阻力特性。实验中我们采用了三种翅片间距(Tp)、三种管排数(Nrow)以及三种管数(Ntube)组成的27种板芯结构,传质实验采用萘升华的方法来进行。然后通过三种限制条件对不同翅片间距、不同管排数和不同管数下的换热板芯的传热性能进行了比较。最后利用最小二乘法得出了具有工程指导意义的准则关联式。     

过渡流下顺排双列圆柱流动、传热特性的数值研究

为了研究过渡流状态下管束传热强化机理,通过基于复合网格的专用程序,本文建立了顺排布置双列管束计算模型。计算结果表明:1)两列圆柱之间的流场结构分为稳定结构(对称死区)和非稳定结构(旋涡),非稳定结构的流场下的下列圆柱传热效率高于稳定结构流场的传热效率。2)由于旋涡的出现,在一定的横向间距内,传热效率升高速率要大于流动阻力升高的速率,大于这个横向间距后,情况相反,这一结果肯定了旋涡不稳定性对下游圆柱壁面传热强化的影响.3)随着纵向间距的缩小,涡脱频率升高,两列圆柱之间流体被加速,加速了旋涡的发展,这能在更小的横向间距内,率先使传热效率升高。     

吸附制冷用吸附单元管设计和传热传质性能研究

本文介绍了一种具有较好传热传质性能的吸附式制冷用吸附单元管,该吸附单元管直接用烟气加热、空气冷却, 可以用于沸石等高温吸附剂。该吸附单元管在加热／冷却流体侧和吸附剂侧均设了翅片,吸附剂内部的传热尺度不大于 2．5 mm,最大传质尺度不大于11 mm。通过数值计算和由吸附单元管组合而成的吸附床的性能初步试验,证明该结构形式的吸附单元管具有优良的传热传质性能。     

水平管降膜蒸发器传热特性研究

建立了水平管降膜蒸发和管内凝结传热实验台,通过对实验结果的归纳,获得了水平管降膜蒸发器总传热系数随喷淋密度、蒸发温度、传热温差和蒸汽入口流速的变化规律,以及管间距对传热特性的影响。结果表明,总传热系数随喷淋密度、蒸发温度的增大而增大,随传热温差的增大而减小,而蒸汽流速对传热系数影响较小;在本文研究的管间距范围内,当管间距为46.7 mm时,总传热系数最高。     

圆翅片叉排热管散热器流动和传热特性数值分析

文中针对三维坐标系下,圆翅片叉排热管散热器的流动和传热特性进行数值模拟研究。分析了三个主要影响因素:翅片间距、翅片厚度和排间距对平均换热系数、流动摩擦系数和热阻的影响。翅片间距分别为6mm、7mm和8mm,翅片厚度分别为0.8mm、1mm和1.2mm,排间距分别为21.7mm、23mm和24.3mm。模拟结果表明:随着迎面风速增加,摩擦系数减小,传热热阻减小;随着翅片厚度的增加,摩擦系数减小、换热能力增强,热阻在大Re时增大明显。随着翅片间距的增大,摩擦系数增大,换热能力提高,热阻增大;随着排间距的增大,摩擦系数在正三角形管排布时的值上下变动,且只有排间距显著增大时,换热能力和热阻才会增大。     

ELECTROHYDRODYNAMIC ENHANCEMENT OF HEAT TRANSFER IN A SHELL-AND TUBE HEAT EXCHANGER

Enhancement of heat transfer in a heat exchanger via a DC corona discharge was studied experimentally using a single-tube shell-and-tube heat exchanger. Air was the working fluid in both the tube and shell sides. Excitation of the tube side was via a single wire electrode, while that of the shell side was via four rod electrodes oriented symmetrically at 90^° intervals. Three series of experiments were performed: (1) excitation of the tube side only, (2) excitation of the shell side only, and (3) simultaneous excitation of the tube and shell sides. Both heat transfer and pressure drop measurements were performed, with Reynolds number and electric field potential as parametric quantities in the tube and shell sides. It was found that highest enhancements take place when the tube and shell sides are excited simultaneously, yielding a 322% increase in the overall heat transfer coefficient. Study of the heat transfer enhancements per unit pumping power indicates that for the range of parameters studied, the technique is most efficient at moderate Reynolds numbers and at electrode potentials in the midrange between threshold and sparkover limits.     

不连续双斜内肋管的管外换热性能

实验和数值研究了不连续双斜内肋管管外的换热性能.在不连续双斜内肋管管外倾斜凹坑的作用下,不连续双斜内肋管和光滑圆管组成的套管内出现了纵向涡流动,雷诺数为30000~90000时比光滑套管换热增强50%,阻力增加60%～70%.     

卧式螺旋管内的沸腾临界后传热

1引言螺旋管由于具有换热效率高、结构紧凑等优点，在各种换热设备中得到了广泛的应用．螺旋管卧式放置时重心低下，适用放航空、航海等航体设备。例如，在新型鱼雷闭式循环热动力系统中，卧式螺旋管圈是其锅炉反应器和凝结器的基本型式。在螺旋管直流式蒸汽发生器中，沸腾临界后（干涸区）传热是不可避免的现象。因此，研究临界后传热，具有十分重要的意义。前人对立式螺旋管内的沸腾传热恶化进行了大量的研究［‘－‘］。但目前对卧式螺旋管的研究相对较少，特别是高干度下的临界传热（干涸区传热），文献中很少见报导。本文对卧式螺旋管…     

螺旋隔板花瓣管换热器的传热强化研究

比较了螺旋用板花瓣管和螺旋隔板低肋管润滑油冷却器和空气冷却器的传热性能,实验结果表明,无论是作为油冷却器,还是作为空气冷却器,螺旋隔板花瓣换热器的综合传热性能明显优于螺旋隔板低肋管换热器,且螺旋隔板花瓣换热器还能节省３０％以上的铜管重量．     

定热流加热管湍流入口段的耦合热流分析

对圆管内物性随温度变化的吸收-各向同性散射介质的湍流入口段,数值研究了定热流加热下辐射与湍流正在发展流耦合换热的稳态热流特征．采用低雷诺数k-ε模型与SIMPLEC算法求解湍流流动与对流换热,采用蒙特卡罗法求解辐射换热;根据耦合换热温度场,采用等权抽样的蒙特卡罗法计算辐射热流。通过模拟计算,给出了介质内的耦合换热辐射热流与导热热流分布。通过分析介质光学厚度、散射反照率、壁面黑度对热流的影响,得出一些有价值的结论．     

HEAT TRANSFER OF ORTHOGONAL-MODE RECIPROCATING TUBE FITTED WITH TWISTED-TAPE

This article describes the results of an experimental study aimed at revealing the heat transfer physics of a twisted-tape insert in a uniformly heated tube for transitional and turbulent flow situations when the test tube remains stationary and reciprocates. Dry air is used as the test fluid, and this study is motivated by the need to understand the effectiveness of twisted-tape inserts on the heat transfer augmentation when applied to the piston cooling of a compression-ignition engine. Prior to the experimental tests, a parametric analysis was performed for which the dimensionless groups that characterized heat convection were identified and adopted to formulate the experimental program and procedures of data reduction. The parametric test matrix involves Reynolds, pulsating, and buoyancy numbers in the ranges 3,000-12,000, 0-0.9, and 0.003-0.009, respectively, with five different reciprocating frequencies tested, namely, 0, 0.83, 1.25, 1.67, and 2 Hz. The nonreciprocating experimental data confirmed considerable heat transfer enhancement due to the twisted-tape insert. When the test tube was reciprocated orthogonally to the main flow direction, both pulsating and reciprocating buoyancy forces arose, which modified the heat transfer from nonreciprocating situations. Initially, a range of heat transfer impediments relative to the nonreciprocating results that could reduce local Nusselt numbers to levels about 75% of nonreciprocating values took place when these reciprocating forces were relatively weak. Further increases of relative strengths of reciprocating forces resulted in subsequent heat transfer recovery and could lead to about 60% heat transfer enhancement relative to nonreciprocating values.     

BOILING HEAT TRANSFER MECHANISMS IN A HORIZONTAL TUBE BUNDLE

The effect of thermal environment on boiling heat transfer performance in a section of a horizontal tube bundle was investigated using R-113 as the working fluid. The in-line tube bundle has five columns and 27 rows with a pitch-to-diameter ratio of 1.3. Heal transfer coefficients obtained from the instrumented tube in the tube bundle with only one tube heated while the other tubes remained unhealed and with all the lubes in the bundle heated are reported for a range of heat flux, pressure, mass flow rate, and quality. The results showed that heat transfer coefficient of a tube in a heated bundle is slightly higher than that in an unhealed bundle, with the variation of heat transfer coefficient decreasing as heat flux, mass flow rate, or pressure increased. It was also found that higher quality would tend to improve the heat transfer. However, the effect of quality disappeared as heat flux, mass flow rate, and pressure increased. Based on the experimental data, the mechanism of the heat transfer augment due to thermal environment was analyzed. It was proposed that fluid agitation and thin liquid film formation are two main factors for a heated bundle to have better transfer performance than an unhealed bundle,     

圆管外石蜡相变蓄热与释热实验研究

建立一小型圆管外石蜡相变蓄热实验系统,对石蜡的蓄热熔化和释热凝固规律进行实验研究.研究石蜡在圆管外不同位置的蓄热熔化规律,自然对流对石蜡蓄热熔化的影响,得出蓄热熔化时间和熔化厚度的优化值.研究石蜡在圆管外不同位置的释热凝固规律,自然对流对石蜡释热过程的影响.     

管壁导热对脉管内自然对流换热影响的研究

本文计算了不同脉管倾角和管壁材料下脉管管壁导热对自然对流换热的影响。发现脉管壁面导热对换热的影响不仅体现在增加了壁面的纯导热部分,更主要的上强化了脉管内的自然对流;壁面和内部气体的温度差异沿脉符轴向的变化是管壁导热强化自然对流的主要原因。     

自然循环加热段内对流传热特性的实验研究

本文以常压去离子水为工质,对自然循环工况下上升加热段内单相水的对流传热特性进行了实验研究。实验结果表明,自然循环工况下上升加热段内工质的物性变化及由浮升力引起的自由流动对对流传热特性有重要影响。通过分析,提出了计算自然循环工况下上升加热段内单相水的对流换热系数的经验关系式。